I've seen that some office windows on high rise buildings use electronic polarization in their glass.  For automobile glass, it would be nice if they made it with a film in it that can dim in a similar way, using a small electronic current.  The technology is there.  I think for safety, you would not put it in the windshield, but the rest of the windows, at just the press of a button, could tint from light to very dark.  If the system had a battery backup, it could use that to power the tinting current while parked.  This would help keep out sun and prying eyes.  I got this idea from watching someone dim a window on a high-rise building.  I thought how many times I wanted to tint the back or side window so that the sun didn't shine into my young daughter's face while she is buckled in.  I think this would be a nice and well used feature in automobiles.